Polymer molding materials are widely used to make a wide variety of materials, including for example various display devices, and, it is often desirable and/or necessary to provide an anti-reflective layer or textured surface therein to inhibit reflected light to ensure satisfactory visibility. Various methods are used to produce such anti-reflective layers and provide a multi-layered film composed of dielectrics having different refractive indices.
Anti-reflection films improve transmission and contrast because they limit saturation of a display by ambient light. By improving display brightness, anti-reflective films can help to reduce power requirements and thereby extend battery life. In addition, minimal reflection ensures that viewers can read their screens more easily, even in bright conditions. Improvement of the brightness, contrast and readability of mobile color displays in PDAs and mobile phones is critical while minimizing power demands.
There is also often a requirement for display films to be electrically conductive in addition to being transparent. This is often for antistatic requirements or to introduce electromagnetic interference (EMI) shielding. Indium tin oxide (ITO) is an example of a transparent conductive material and is one of the materials that makes the magic of flat panel displays (monitors, televisions, etc.) possible. When sputtered onto a solid substrate in a thin layer, it acts as a transparent conductive film.
ITO coatings have found many applications in the display and optical coatings industries as transparent conductors. ITO is optically transparent like glass, but unlike glass it is electrically conducting and, therefore, capable of carrying an electric current. ITO films are used in numerous electronic devices, such as liquid crystal displays (LCDs) and plasma television screens. More recently, ITO films have also been used as conductive coatings on photovoltaic cells, commonly called solar cells. Processing conditions for ITO are important because they can significantly affect film conductivity. The key is to increase conductivity while retaining transparency in the visible spectrum. The conductivity creates absorption in the infrared due to free carriers.
A problem with the use of transparent conductive materials such as ITO, is that due to the very high refractive index of ITO, such ITO coatings are highly reflective, which restricts viewability. In addition, high reflection implies low transmission from a free standing film, which manifests itself as low brightness for the display. Therefore, a requirement for ITO layers has serious implications for both viewer comfort and brightness (power requirements) of a display.
Various processes have been suggested to get around this problem by using multilayer coatings to provide some level of anti-reflection performance. However, these multilayer coatings are often mixed metal oxides to provide layers of varying refractive index, tuned to provide optimal reflection and transmission characteristics for the total construction. This can be an expensive and time consuming process. Thus, it would be desirable to provide a method of making a transparent conductive oxide coating, such as an ITO coating, itself anti-reflective without the need for additional layers.